Image quality improvement for liquid crystal displays

Abstract

A liquid crystal display (LCD) system, comprising a matrix of pixels, analyzes a video data stream for grayscale level jumps from extreme black to moderate gray levels. Transitions in grayscale levels are restricted between adjacent pixels so as to reduce image degradation due to fringe field effects. A memory, such as a plurality of shift registers, may be used to store grayscale levels of adjacent pixels which are compared and if a ratio between these grayscale levels exceeds a desire value then at least one of the grayscale levels is modified.

What is claimed is:  
     
       1. A system for improving image quality of a liquid crystal display (LCD), said system comprising: 
       a matrix of pixels arranged in a plurality of columns and a plurality of rows, wherein an intersection of a row and a column defines a location of a pixel in said matrix;  
       at least one digital-to-analog converter (DAC) having a digital input and an analog output;  
       a plurality of column switches adapted for coupling the analog output of said at least one DAC to each of said plurality of columns;  
       a plurality of row switches adapted for selectively coupling each of said plurality of rows to said plurality of columns;  
       column control logic for controlling said plurality of column switches;  
       row control logic for controlling said plurality of row switches;  
       a video frame to gray scale conversion and pixel address logic for converting video information into LCD gray scale values and corresponding pixel address locations thereof; and  
       video data comparator/modifier logic, said video data comparator/modifier logic adapted to receive the LCD gray scale values for each pixel of the matrix of pixels, wherein gray scale values of adjacent pixels are compared and if a ratio of the gray scale values of adjacent pixels is greater than a desired value, then one of the gray scale values is modified so that the ratio of adjacent pixel gray scale values is no greater than the desired value;  
       said video data comparator/modifier logic is adapted for sending all unmodified gray scale values and any modified gray scale values to said at least one DAC;  
       said video frame to gray scale conversion and pixel address logic adapted for sending said pixel address locations to said column control logic and said row control logic.  
     
     
       2. The system of  claim 1 , wherein the desired value is two. 
     
     
       3. The system of  claim 1 , further comprising a video memory for storing said LCD gray scale values. 
     
     
       4. The system of  claim 1 , further comprising a video memory for storing said unmodified and said modified LCD gray scale values. 
     
     
       5. The system of  claim 1 , further comprising a video memory coupled to said video data comparator/modifier logic. 
     
     
       6. The system of  claim 1 , wherein said video data comparator/modifier logic comprises a plurality of registers adapted for storing gray scale values for at least N adjacent pixels. 
     
     
       7. The system of  claim 6 , wherein said video data comparator/modifier logic comprises a level writing decision logic for determining the ratio of the adjacent pixel LCD gray scale values. 
     
     
       8. The system of  claim 7 , wherein said level writing decision logic determines which of said LCD gray scale values are to be modified. 
     
     
       9. The system of  claim 6 , wherein N is equal to eight. 
     
     
       10. The system of  claim 6 , wherein N is equal to six. 
     
     
       11. The system of  claim 6 , wherein N is equal to ten. 
     
     
       12. The system of  claim 6 , wherein N is selected from the group consisting of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16. 
     
     
       13. The system of  claim 1 , further comprising a gray scale look-up table coupled between said video data comparator/modifier logic and said at least one DAC. 
     
     
       14. The system of  claim 1 , wherein said LCD, said plurality of column switches and said plurality of row switches are fabricated on a semiconductor integrated circuit. 
     
     
       15. The system of  claim 1 , wherein said LCD, said plurality of column switches, said plurality of row switches, said column control logic, and said row control logic are fabricated on a semiconductor integrated circuit. 
     
     
       16. The system of  claim 1 , wherein said video frame to gray scale conversion and pixel address logic, said video data comparator/modifier logic and said at least one DAC are fabricated on at least one semiconductor integrated circuit. 
     
     
       17. A method for improving image quality of a liquid crystal display (LCD) comprising a matrix of pixels arranged in a plurality of rows and columns, wherein an intersection of a row and a column defines a position of a pixel in the matrix, said method comprising the steps of: 
       determining if a ratio of gray scale values of adjacent pixels is greater than a desired value, wherein;  
       if the ratio is less than or equal to the desired value, then writing the gray scale values to the adjacent pixels, and  
       if the ratio is greater than the desired value, then modifying one of the gray scale values of the adjacent pixels so that the ratio is less than or equal to the desired value, and then writing a gray scale value and the modified gray scale value to the adjacent pixels.  
     
     
       18. The method of  claim 17 , further comprising the steps of: 
       receiving video information; and  
       converting the video information into the LCD gray scale values and the corresponding pixel address locations thereof.  
     
     
       19. The method of  claim 17 , further comprising the step of storing the LCD gray scale values and modified gray scale values in a memory. 
     
     
       20. The method of  claim 17 , further comprising the step of storing the gray scale values of adjacent pixels in a plurality of registers. 
     
     
       21. The method of  claim 20 , further comprising the step of storing the modified gray scale values of adjacent pixels in some of the plurality of registers.